When a man page is in data_files, the rpm installer
compresses it with gzip (done by the brp-compress
script). I attached a little hack for
install_data command to add a ".gz" to such man pages.
Then it works for me.

Of course, the proper fix would be to detect if
brp-compress is run and what files were compressed by
the script. But I am not an rpm guru, so its up to you
how you want to fix it.

I am using a Debian Linux unstable boxen with Python
2.2.2-2, and rpm 4.0.4-11